In many cases spraying equipment is used to apply paint to surfaces. The types of spraying equipment available are divided into three categories. The first category sprays paint using high volumes of air at low pressures. The second category sprays paint using air at high pressures. The third is airless, relying solely on pressurised paint.
One example of the first category of sprayer has an air supply to which is attached a hose having a gun at the free end thereof. The gun is provided with a trigger mechanism which is arranged to open and close a nozzle mounted in the gun. Around the nozzle there is provided a plurality of holes through which air is expelled. Within this air stream is a region of low pressure. A container holding a supply of paint is attached to the gun. A pipe extends from the gun into the container. Opening the nozzle causes paint to be drawn from the container through the pipe into the gun, and to be expelled from the nozzle.
This type of spraying equipment suffers from a number of drawbacks. Relying on the venturi effect to lift the paint from the container into the gun is satisfactory for some paints, but is not satisfactory where the paints are of high viscosity, such as emulsions. This type of spraying equipment simply cannot provide sufficient lift to draw this type of paint from the container to the gun and subsequently out of the nozzle.
A number of other problems associated with this type of spraying equipment arise from the location of the container. Because the container is carried on the gun itself, which is hand held, the sprayer operator must bear the weight of the paint and the container whilst he is spraying. Clearly, carrying such a weight leads to fatigue in the wrist. This fatigue may result in the sprayer operator taking more rest periods than he would if he did not have to carry such a weight. However, and more seriously, the continued use of such a sprayer could have longer term health risks, such as repetitive strain injury.
The fact that the container is attached to the gun makes the gun/container assembly a larger object then the gun alone. This makes it difficult to spray paint in corners or other concealed areas. Additionally, when spraying paint on to substantially horizontal surfaces an uneven spray pattern can be produced because the gun cannot be held so that the nozzle is at a right angle to the surface to be painted. If the gun is held at a right angle to the surface to be painted, paint cannot be drawn out of the container. It is therefore necessary to direct the gun at an angle of not more than 60 degrees to the surface being sprayed but this causes the spray pattern to be uneven.
An example of the second category of spraying equipment comprises a hose extending from a remote supply of pressurised air, the hose having a gun at the free end thereof on which there is mounted a container filled with paint. The gun is similar to the type described above insofar as air is used to draw paint through the gun, but the orifices tend to be smaller. In order to draw the paint through the gun the air must be pressurised to a high pressure, and must be held in a pressurised vessel.
The third category of spraying equipment is a variation of the second. A high pressure system pressurises the paint and the gun has a nozzle that can be opened or closed to permit or prevent the fluid passing through the nozzle. The paint need not be held in a pressurised vessel but can be held in an open container from which it is drawn by pumping means. It is then pressurised in the hose to very high pressures.
Although these types of sprayer generate sufficient pressure to spray viscous substances such as emulsion paints, the apertures in the nozzle of the gun tend to be much smaller than the apertures in the nozzles of the guns used with high volume low pressure systems. This can lead to the apertures becoming blocked with paint.
Another problem associated with high pressure low volume sprayers is that the paint hits the surface to be coated at such a high velocity that some of the paint bounces off the surface. Not only does this contaminate the air space in which the spraying is being carried out, but also objects other than the object at which the spray is aimed are covered in paint. Additionally, high pressure low volume spraying equipment tends to be heavy and difficult to manoeuvre.
Guns used with spraying equipment often provide for regulating the degree to which the liquid outlet may be opened. Prior art guns rely on adjusting the position of a spring against which an obturating member is moved to achieve this regulation. However, this adversely affects the feel of the trigger.
It would therefore be desirable to provide spraying equipment which does not suffer from the above-mentioned disadvantages.
It would also be desirable to provide a gun which does not suffer from the problems encountered by available guns.